1. Field of the Invention
The present invention is in the field of refrigerated cabinet doors, and specifically relates to devices for holding such doors in a desired open position.
2. The Prior Art
The doors of a refrigerated display cabinet are generally urged shut by torsion springs to prevent them from being inadvertently left in the open position with consequent inflow of warm air. Nevertheless, it is desirable to retain the door in an open position when the cabinet is being stocked from the front. Further, shoppers carrying packages find it more convenient if the door can be held in an open position while they are removing merchandise from the cabinet. Thus, the present invention is directed to a device which holds the door in a selectible open position but which otherwise does not interfere with its normally urged closed operation.
A number of hold open mechanisms are known in the art. The most elementary type of hold open consists of a wedge or a block member inserted between the door frame and the door mounting frame in the vicinity of the hinge axis. Because of this location, the devices are subject to great forces owing to the leverage exerted on them by the forces applied to the door. As a result, such devices may damage the door frame, the door mounting frame, and/or the hinges. Certain prior art devices must be manually set into position each time the door is to be held open. This is obviously undesirable if the hold open is used with any frequency.
A more sophisticated hold open known in the prior art uses an arm which is pivoted to the door frame some distance from the hinge axis for rotation in a plane perpendicular to the hinge axis and whose other end is connected to a pin which slides in a channel mounted in or on the door mounting frame. As the door is opened, the pin slides along the channel toward the hinge axis, and it is known in the art to provide one or more slots in the edge of the channel into which the pin can be urged to hold the door open at a designated angle.
A particular hold open of the type just described further comprises an arrestor attached to the channel for limiting the motion of the door and for detenting it in the widest open position. The arrestor includes a slotted planar sheet metal detent attached to the end of the channel nearest the hinge axis with its slot aligned with the channel, and having a portion at its end nearest the hinge axis bent around the end of the channel to prevent misalignment of the slot with the channel. Because a portion of the sheet metal detent is bent around the end of the channel, it is not convenient to alter the position of the arrestor along the channel to selectively vary the widest open position of the door.
The edges of the slot in the sheet metal detent define a guideway extending along the channel. The edges of the slot are arched inwardly toward each other over a portion of their length to define a constricted portion in the guideway. The width of this constricted portion is required to be slightly less than the width of the pin. As the pin moves along the channel, it enters the guideway, and upon encountering the constricted portion of this guideway, it forces the edges of the slot apart, deforming the sheet metal detent. After the pin has passed the constricted area, the edges of the slot spring together thereby yieldably retaining the pin within the slot. Forces applied to the door in closing it are normally sufficient to overcome the opposition of the detent.
The opposition of the detent slot to motion of the pin serves to warn the person opening the door that the hold open position is being approached, and it further serves to dissipate the momentum of the swinging door.
This type of device is useful in applications where the door is not opened to its detented position very frequently. However, in those applications where the door is opened to its detented position many times each day, it has been found that the edges of the planar sheet metal detent slot and the pin body engaging are both worn away owing to the substantial contact pressures produced as the pin engages the edges of the slot spreading them. As a result, the useful life of the device is shortened.
Another drawback resulting from the excessive stiffness of the planar sheet metal detent in resisting spreading is the necessity for closely controlling the width of the slot relative to the width of the pin. If the slot is undersize, excessive force will be required to drive the pin into the slot, while if the slot is too large, it will not either adequately oppose the motion of the pin or hold the door in an open position.
There is therefore need for a door hold open mechanism that can be used potentially hundreds of times each day without incurring excessive wear or requiring components to be held to precise tolerances.